There are more than 200 satellites in our solar system, but their relatively small size makes similarly sized extrasolar satellites (exo-solar satellites) very difficult to detect with current equipment. So far, the best exomoon candidates are two roughly Neptune-sized objects orbiting the Jupiter-sized exoplanets Kepler-1625b and Kepler-1708b, but their existence is debated. In the new study, astronomers reanalyzed the Hubble and Kepler data used to identify these two exomoon candidates.
Artist’s impression of Kepler 1625b, a gas giant planet with a large moon, Kepler 1625b-i. The pair has a similar mass-to-radius ratio as the Earth-Moon system, but is magnified by a factor of 11. Image credit: Sci.News.
From Galileo Galilei’s discovery of Jupiter’s four major moons in 1610, which sparked the Copernican Revolution, to cryovolcanic activity on Saturn’s moon Enceladus as evidence of the continuation of liquid water-based chemistry in the outer Solar System. Until their discovery, satellites continue to play a fundamental and important role. Interesting insights into planetary science.
Therefore, the detection of satellites around some of the thousands of exoplanets known today has been eagerly anticipated for more than a decade.
So far, two possibilities for exomoon detection have been raised, both originally claimed with data from NASA’s Kepler space mission.
The first candidate corresponds to a Neptune-sized satellite in a wide orbit around the Jupiter-sized planet Kepler-1625b, which orbits the evolved Sun-like star Kepler-1625 for 287 days.
A second exomoon claim was recently announced by the same team. It is located around the Jupiter-sized planet Kepler-1708b and is in a 737-day orbit around the solar-type main sequence star Kepler-1708.
“Exomoons are so far away that even the latest and most powerful telescopes cannot directly see them,” said Dr Rene Heller, an astrophysicist at the Max Planck Institute for Solar System Research.
“Instead, telescopes record fluctuations in the brightness of distant stars, and the time series is called a light curve.”
“Astronomers then look for signs of the moon in these light curves. When an exoplanet passes in front of the star as seen from Earth, it dims the star ever so slightly.”
“This phenomenon is called a transit, and it repeats periodically as the planet orbits the star.”
“Earth-associated exomoons will have a similar dimming effect. But their signature in the light curve will not only be significantly weaker.”
“As the moon and planet move around each other’s center of gravity, further dimming of this light curve will follow a fairly complex pattern.”
“There are also other effects to consider, such as planetary and lunar eclipses, natural brightness changes in stars, and other noise sources produced during telescopic measurements.”
To detect exomoons, Dr. Heller and his colleague, Dr. Michael Hipke of the Sonneberg Observatory, have to figure out all possible sizes, mutual distances, and orbital orientations of possible exoplanets and their moons. We calculated a million “artificial” light curves.
We then compared these simulated and observed light curves and looked for the best match.
They used the open source algorithm Pandora. It is optimized for searching examoons and can solve this task orders of magnitude faster than previous algorithms.
In the case of Kepler-1708b, the authors found that the moonless scenario explained the observed data as accurately as the moon scenario.
“The probability of a satellite orbiting Kepler-1708b is clearly lower than previously reported,” Hipke said.
“This data does not suggest the presence of exomoons around Kepler-1708b.”
“There’s a lot to suggest that Kepler-1625b also doesn’t have a massive companion star.”
“This planet’s stellar forward transit has been previously observed with the Kepler and Hubble telescopes.”
The researchers argue that instantaneous changes in the star’s brightness across the disk, an effect known as stellar edge darkening, are crucial to the proposed exomoon signal. There is.
“For example, the edge of the solar disk appears darker than the center,” the researchers said.
“However, this edge-darkening effect looks different depending on whether you look at Kepler-1625b’s host star with the Kepler telescope or the Hubble telescope.”
“This is because Kepler and Hubble are sensitive to different wavelengths of light they receive.”
“Our modeling of this effect explains the data more conclusively than a giant exomoon.”
team’s paper It was published in the magazine natural astronomy.
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R. Heller and M. Hipke. It is unlikely that Kepler-1625b and Kepler-1708b have large exomoons around them. Nat Astron, published online on December 7, 2023. doi: 10.1038/s41550-023-02148-w
Source: www.sci.news
